Assessment of MODIS-derived indices (2001–2013) to drought across Taiwan’s forests

Abstract

Tropical and subtropical ecosystems, the largest terrestrial carbon pools, are very susceptible to the variability of seasonal precipitation. However, the assessment of drought conditions in these regions is often overlooked due to the preconceived notion of the presence of high humidity. Drought indices derived from remotely sensed imagery have been commonly used for large-scale monitoring, but feasibility of drought assessment may vary across regions due to climate regimes and local biophysical conditions. Therefore, this study aims to evaluate the feasibility of 11 commonly used MODIS-derived vegetation/drought index in the forest regions of Taiwan through comparison with the station-based standardized precipitation index with a 3-month time scale (SPI3). The drought indices were further transformed (standardized anomaly, SA) to make them better delineate the spatiotemporal variations of drought conditions. The results showed that the Normalized Difference Infrared Index utilizing the near-infrared and shortwave infrared bands (NDII6) may be more superior to other indices in delineating drought patterns. Overall, the NDII6 SA-SPI3 pair yielded the highest correlation (mean r ± standard deviation = 0.31 ± 0.13) and was most significant in central and south Taiwan (r = 0.50-0.90) during the cold, dry season (January and April). This study illustrated that the NDII6 is suitable to delineate drought conditions in a relatively humid region. The results suggested the better performance of the NDII6 SA-SPI3 across the high climate gradient, especially in the regions with dramatic interannual amplifications of rainfall. This synthesis was conducted across a wide bioclimatic gradient, and the findings could be further generalized to a much broader geographical extent.

Assessment of Plant Communities and Identification of Indicator Species of an Ecotonal Forest Zone at Durand Line, District Kurram, Pakistan

“…The soil micro and macro nutrients level can significantly affect species richness and communities Byrne et al (2017) examined plant's responses against precipitational change and concluded comparatively high level sensitivity. Chang et al (2018) and Skagen et al (2018) emphasized forest sensitivity and responses against precipitation variation in ecotones over a time scale.…”

Remotely sensed assessment of increasing chronic and episodic drought effects on a Costa Rican tropical dry forest

“…Annual anomalies of precipitation and temperature of the overlapping time period , defined as the difference between the long-term mean and each year, were calculated. We also calculated the Standardized Precipitation Index (SPI) (Hirschi et al 2011) using the SPI Generator (University of Nebraska-Lincoln, NE, USA) to assess the interannual meteorological drought (Zou et al 2020) solely using monthly precipitation data (for details, see Chang et al (2018)). The SPI may be formed at different temporal resolutions (e.g., three months [SPI-3] to highlight seasonal variation) (Ji and Peters 2003); we derived the SPI-6 specifically for the distinct wet (May-October) and dry (November-April) seasons.…”

The Dynamic of Vegetation Growth with Regular Climate and Climatic Fluctuations in a Subtropical Mountainous Island, Taiwan

“…Taiwan, a humid subtropical mountainous island with high annual precipitation (MAP) approximate 2500 mm year −1 , has experienced an amplifying seasonal rainfall and droughts (i.e., drier winter-spring and wetter summer), and regional discrepancies between wetter northern Taiwan and drier southern Taiwan over the past century [52,53]. Studies have demonstrated that the El Niño events during the preceding winter (November-February) will bring abundant rainfall for the following spring and summer seasons in Taiwan, and vice versa for La Niña events [54,55].…”